Graphene films have excellent carrier mobility, wide-band optical transmittance, thermal conductivity and flexibility. As a novel material, grapheme films have important application prospects in the field of photonics and optoelectronics, such as flexible display devices, detectors, solar cells and so on. From appearance of single-layer graphene electronic components to the industrialization of graphene films, one of the keys is the development of patterning of the graphene film, that is, the preparation of cells and arrays with certain geometric or functional structures, which is necessary for fundamental research on graphene as well as the industrial application of large-scale integrated devices such as photonics and optoelectronics.
At present, the following methods are mainly adopted for patterning of the graphene film:
(1) micro/nano structure patterns are prepared by electron beam exposure or micro-nano processing techniques such as optical exposure and reactive ion etching. This method may realize pattern precision of several nanometers by developing the patterning of graphene film, and thus is widely used in advanced fundamental science research. However, this method takes the surface of a graphene spin-coated with organic photoresist as a photosensitive layer, which inevitably introduces organic gel contamination and thus making the graphene film worse. In addition, this method for developing the patterning of graphene film is complicated and expensive, and thus has not been adopted by enterprises in the industrialization process of graphene film.
(2) patterning of graphene film by “direct writing” with laser. This method utilizes a laser beam to directly etch a pattern on a graphene film, which has a simple operation and a fast etching rate and may protect from photoresist contamination, and thus is favored by enterprises in the industrialization process of graphene film. However, when the laser propagates in free space, it generally has a spot of several tens of micrometers, which may directly affect the line width and precision of the etched graphene film pattern. In order to obtain high-quality graphene film patterns, pulsed lasers with high-performance are adopted whenever possible, such as the use of expensive femtosecond lasers in science research. At present, the size of pattern structure obtained by the production enterprise such as 2d Carbon by using picosecond pulse laser etching is generally above 30 μm. In addition, during the patterning process performed on the graphene film by pulsed laser, it also etches a certain surface of the substrate supporting the graphene film, which not only pollutes the graphene film to a certain extent, but may also impact the applications in the field of photons and optoelectronics negatively.
(3) the hard mask is disposed on the graphene film, and the patterning thereof is directly performed by reactive ion etching. This method was recently proposed by Keong Yong et al., which is capable of implementing a pattern structure in tens of micrometers (Scientific Reports, Vol. 6, 24890, 2016). However, due to the undercut effect of the etched ions, the graphene film obtained by this method has defects in the range of about twelve micrometers from the edge. In addition to that, reactive ion etching may also damage the substrate material. In addition, the reaction area of a reactive ion etching apparatus is generally in a range of several inches, which may cause new and difficult problems in technical terms for large-area of graphene film patterning with tens of inches, and it is not suitable for industrialization promotion due to the expensive price.
Ultraviolet photo-oxidation methods are widely used for cleaning substrate materials. It uses vacuum ultraviolet light to decompose oxygen molecules to oxygen excitons and ozone, etches organic materials or carbon family materials by using strong oxidizing properties of the oxygen excitons, and releases gas of carbon dioxide or carbon monoxide. In the past few years, ultraviolet photo-oxidation methods are used for modifying the graphene film to obtain graphene with certain nanostructure and oxygen-containing functional groups. However, compared with reactive ion etching, ultraviolet photo-oxidation has weak reaction intensity at room temperature, which is not suitable for patterning of large-area graphene films. In order to increase the strength of the ultraviolet photo-oxidation etching, a self-developed ultraviolet photo-oxidation high vacuum equipment (ZL201210462171.7, ZL201210442424.4) is adopted, which significantly increases the strength of oxidation etching for the graphene film by heating the substrate to 120° C. However, due to the enhanced oxygen exciton diffusion ability during high-temperature ultraviolet photo-oxidation, the pattern structure of the graphene film is highly distorted, and the surface of the graphene near the edge is severely damaged. The xenon lamp excimer light source may emit ultraviolet light with wavelength of 172 nm, which may oxidize most of the organic molecules and has stronger oxidizing, and thus may etch eight to ten layers of graphene at room temperature.
In the present disclosure, the patterning of the graphene film with micron structure is realized by using a xenon lamp excimer ultraviolet photo-oxidation. In order to further improve the steepness of pattern structure of the graphene film and reduce the damage of etching of the oxygen excitons to the graphene at the bottom of the mask along the direction of the graphene film, the motion directivity of the oxygen excitons in a vertical direction is restrained by applying a magnetic field in the vertical direction, and thus the damage caused by etching of the oxygen exciton to the graphene film is reduced, improving the quality of the graphic structure of the graphene film. By using the magnetic field to regulate the moving direction of the oxygen excitons, a pattern with a pattern structure different from that of the mask pattern may be obtained, and thus the purpose of adjusting the graphic structure of the graphene film may be achieved.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.